The larvae of most species develop in all sorts of organic matter of animal origin, in particular in droppings and dung, carrion, and nests of birds; only a few species can develop in other decaying media, including rotten fungi or plant matter. Adults usually occur on or near the breeding substrates, but visit flowers as well, with a preference for umbellifers. The species of Carnus live exclusively in the nests of birds, especially those breeding in bushes, trees and in (tree)holes, where the larvae feed on nest debris. The adults emerge from the pupa with normal wings, fly about until they have found another suitable nest and then shed their wings. They attach themselves to the nestlings and feed on the flakes and moisture of their skin, and they are suspected to feed on blood as well.